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MIL-HDBK-1038
vertical frames interposed between the end trucks and the bridge girders.  In the
case of the semi-gantry cranes, only one end is so configured the other end is a
typical bridge crane running on an elevated rail.  They are not limited by any
overturning moment due to rated load and may be of any capacity that the rails can
support.
Since the only structural support that is required for gantry cranes is a
pair of ground level rails, they can be installed in buildings without the major
investment of an overhead runway.  Semi-gantry cranes are well suited to outdoor
installations such as plate yards adjacent to
buildings one end running on a ground level rail and the other on a high rail
near the top of the wall.
Gantry and semi-gantry cranes offer broad design flexibility and can be
configured for many varied functions.  The bridge structure may be of the double
girder arrangement with an overrunning trolley or a single girder with an
underrunning hoist/trolley unit.  Crane controls may be located in an operator's
cab (on a sill beam, bridge, or trolley) or on a pendent pushbutton station.
2.8.1
General Description.  The bridge structure is designed to the same
criteria as the OET and underrunning cranes, whichever is applicable to the
particular configuration.  The upper part of the vertical frame serves as an end
tie for the bridge girders.  The lower end of the vertical frame incorporates a
sill beam with a two-wheel end truck at each end.  Sturdy braces between the
vertical frames and the bridge girders provide the required strength and rigidity
to the gantry structure.  All crane motions are driven by electric motors.
Electric power is transferred from a fixed location at the elevation of the bridge
girders to the crane by means of collector shoes sliding along rigid conductors
parallel to the bridge girder end ties.
Virtually all large capacity gantry and semi-gantry cranes are custom
designed.  Figures 12 and 13 show the gantry and semi-gantry configurations,
together with some of the available options.
2.8.2
Distinctive Features.  Large capacity gantry cranes (usually 40 tons or
greater) are sometimes powered by an on-board diesel engine-electric
generator set which is mounted on the sill beam.  When an operator's cab is
provided, it is most often placed on the sill beam.  However, depending on the
intended service, the operator's cab may be installed on a bridge girder or the
trolley.
These cranes can be configured to provide limited capacity outboard of
the runway rails by the use of vertical frames with an open center.  This
arrangement, sometimes called "through-leg", may be used with either overrunning
or underrunning trolleys and hoist/trolley units.
Standard commercial rubber-tired gantry cranes are often used in
container handling operations.  The maximum practical height limits the stacking
height to three containers.
2.8.3
Industry Standards.
The governing industry standard for gantry (and
semi-gantry) cranes is CMAA Specification #70, Specification for Top Running
Bridge and Gantry Type Multiple Girder Electric Overhead Traveling Cranes,
published by the Crane Manufacturers Association of America, Inc.  The safety
aspects of the design and operation are addressed in ANSI/ASME B30.2, Overhead
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